Problem: Emily is 3 times as old as Umaima and is also 20 years older than Umaima. How old is Emily?
Explanation: We can use the given information to write down two equations that describe the ages of Emily and Umaima. Let Emily's current age be $e$ and Umaima's current age be $u$ $e = 3u$ $e = u + 20$ Now we have two independent equations, and we can solve for our two unknowns. One way to solve for $e$ is to solve the second equation for $u$ and substitute that value into the first equation. Solving our second equation for $u$ , we get: $u = e - 20$ . Substituting this into our first equation, we get the equation: $e = 3$ $(e - 20)$ which combines the information about $e$ from both of our original equations. Simplifying the right side of this equation, we get: $e = 3e - 60$ Solving for $e$ , we get: $2 e = 60$ $e = 30$.